The present invention relates to apparatus incorporating balloons and to techniques employing balloons.
Certain medical and veterinary procedures employ balloons mounted on catheters for various purposes. For example, as described in co-pending, commonly-assigned U.S. patent application Ser. No. 09/905,227, published as U.S. Pat. No. 2002/0065512-A1, the disclosures of which are hereby incorporated by reference herein, a structure including a balloon is used as a reflector for directing ultrasonic energy from an ultrasonic transducer mounted within the balloon onto a region of tissue to be ablated. As further described in the aforementioned application, the balloon structure also focuses the ultrasonic energy. Such a device can be used, for example, to ablate cardiac tissue in treatment of cardiac arrhythmias. Other balloon structures are used for other medical and veterinary procedures.
Typically, the balloon is placed within the body of the subject by threading a carrier catheter having the balloon attached thereto into the body of the subject through the vascular system or other passages within the body and into the desired treatment location with the balloon in a deflated condition. Once the balloon is at the desired location within the subject""s body, the balloon is inflated, the desired procedure is performed and the balloon is again deflated and withdrawn by withdrawing the carrier catheter. In many procedures, it is desirable to maintain alignment between portions of the balloon, and to maintain alignment between features of the balloon and the carrier catheter while the balloon is in an inflated condition. For example, in certain preferred embodiments taught in the aforementioned ""227 application, the ultrasonic transducer is mounted on a portion of the carrier catheter disposed within the balloon adjacent a proximal end of the balloon. The ultrasonic transducer is generally cylindrical and is coaxial with the carrier catheter. When the balloon is in an inflated condition, the proximal to distal, or lengthwise, axis of the balloon should also be coaxial with the transducer for optimum focusing of the ultrasonic energy.
It would be desirable to provide a rigid reinforcing element which extends between the carrier catheter or ultrasonic transducer and the distal end of the balloon, so as to prevent tilting of the balloon or deformation of the balloon in radial directions, transverse to the lengthwise or proximal to distal direction of the carrier catheter and transducer. However, it is also necessary to allow some flexibility of the balloon in the radial directions when the balloon is deflated to allow threading of the catheter during insertion and withdrawal. The balloon must bend in the radial directions to follow the curves of the vascular system or other body passages.
Some devices which employ balloons also require a passage through the balloon. For example, in many procedures, the threading operation relies on a guide wire which is threaded through the lumen of the carrier catheter and out through the distal end of the structure into the vascular system. After the guide wire is threaded, the catheter, with the balloon thereon, is advanced along the guide wire. In other situations, it may be desirable to introduce structures such as sensing electrodes or other instruments, anchoring elements or the like through the lumen of the catheter and advance these structures so that they project beyond the distal end of the balloon.
Ordinarily, the proximal end of the balloon is affixed to the carrier catheter. As further explained below, the balloon tends to expand in radial directions transverse to the lengthwise direction and to contract in the lengthwise direction when inflated. Thus, the distal end of the balloon should be free to move relative to the carrier catheter in the lengthwise direction during inflation and deflation. Simply providing an extension of the carrier catheter projecting distally through the balloon and through the wall of the balloon at the distal end will not allow for such movement unless a sliding seal is provided at the juncture of the carrier catheter and the distal end. Such a sliding seal increases the bulk of the assembly in the deflated condition and introduces significant reliability issues. Thus, there exists a need for a better structure to provide a lumen or bore extending through the interior of the balloon.
Apparatus according to one aspect of the present invention includes a balloon having proximal and distal ends and a lengthwise direction between the ends. The balloon has a deflated length between its ends in the deflated condition and an inflated length in an inflated condition, the inflated length being less than the deflated length. Apparatus according to this aspect of the invention also includes a plurality of engagement elements disposed at least partially within the balloon. These elements are moveable with respect to one another in the lengthwise direction. As the balloon contracts in the lengthwise direction upon inflation, the balloon urges the engagement elements into engagement with one another. However, the engagement elements are moveable away from one another in the lengthwise direction upon deflation of the balloon. Apparatus according to this aspect of the invention desirably also includes an axial member extending in the lengthwise direction within the balloon, at least one of the engagement elements being slideable along the axial member to bring the engagement elements into and out of engagement with one another. The axial member most desirably is a flexible member. Most preferably, the axial member includes a spring as, for example, a coil spring, and the spring acts to urge the proximal and distal ends of the balloon away from one another when the balloon is inflated. For example, the engagement element may be small tubular elements surrounding the coil spring.
Most preferably, apparatus according to this aspect of the invention also includes a carrier catheter having a lumen. An end of the balloon, most preferably the proximal end of the balloon, is secured to the carrier catheter. The engagement elements may include a stop member secured to the carrier catheter and disposed within the balloon adjacent the proximal end thereof. The engagement elements desirably include a first or proximal movable engagement element which engages the stop when the balloon is in its inflated condition. Apparatus according to this aspect of the invention allows the balloon to flex in directions transverse to the lengthwise direction of the carrier catheter while the balloon is deflated and while the engagement elements are remote from one another. However, when the balloon is inflated, the engagement elements are forced into engagement with one another so as to provide a rigid support extending lengthwise within the balloon. The support limits or prevents deflection of the distal end of the balloon in the radial directions relative to the proximal end of the balloon and relative to the carrier catheter, thereby maintaining the balloon in alignment with the carrier catheter.
The axial member within the balloon may incorporate a tube. Desirably, the tube is distensible in the lengthwise direction. A proximal end of the tube is mechanically linked to the proximal end of the balloon. For example, the proximal end of the tube may be mechanically connected to the carrier catheter or to the stop, so that the interior bore of the tube communicates with the lumen of the carrier catheter. The distal end of the tube is mechanically linked to the distal end of the balloon. Thus, when the balloon is deflated, the tube is stretched in the lengthwise direction. When the balloon is inflated, the tube is shortened in the lengthwise direction. The tube cooperates with the lumen of the catheter so as to provide a continuous passage extending through the lumen of the catheter and out through the distal end of the balloon. Most preferably, the tube is formed from material as, for example, an expanded polymer, so that the diameter or radial dimensions of the interior bore do not decrease substantially when the tube is stretched in the lengthwise direction. Thus, the continuous passage remains fully functional in all conditions of the balloon. This facilitates use of the assembly with guide wires or other instruments which must protrude beyond the distal end of the balloon.
These and other objects, features and advantages of the present invention will be more readily apparent from the detailed description of the preferred embodiments, set forth below, taken in conjunction with the accompanying drawings.